1. Field of the Invention
The present invention relates to a device for positioning a coupling means in a gearbox in a first gear position, a second gear position and an intermediate neutral position. The invention also relates to a method for such positioning of a coupling means in a gearbox.
The invention is described hereinbelow configured so that the gearbox includes a dropbox or transfer gearbox that is operationally connected to a main gearbox. Such an arrangement with a main gearbox and a transfer gearbox is found in a construction machine such as a dumper or wheel loader. The purpose of the transfer gearbox is to allow shifting between a low-gear register (low) and a high-gear register (high), and also to distribute the force between a front axle and a rear axle of the vehicle. It should be appreciated, however, that this is a preferred, but in no way limiting, application of the invention.
Using conventional technology, shifting between low and high can be performed only when the vehicle is standing still. It is desirable for it to be possible to perform such shifting while driving (traveling) and thereby obtaining shorter operating cycle times.
2. Background Art
U.S. Pat. No. 4,593,606 describes a piston/cylinder device for bringing about shifting action in a gearbox. A main piston is enclosed in a first working cylinder of a housing and connected to a piston rod. The piston rod is in turn connected to a coupling means for the purpose of bringing about such shifting. A rear portion projecting from the main piston forms a second working cylinder, in which an auxiliary piston is displaceably arranged. A first pressure chamber is formed between the main piston and a first end of the first working cylinder. A pressure chamber is formed between the mutually facing surfaces of the main piston and the auxiliary piston. A pipe for compressed air leads to the second pressure chamber through the auxiliary piston. A third pressure chamber is formed between the auxiliary piston and a second end of the first working cylinder.
Devices that are equipped with such a piston/cylinder device are relatively complicated with two working cylinders. Furthermore, a relatively complicated control of the supply of compressed air is required in order to achieve the three positions.